1. Field of the Invention
The present invention relates to an image processing technique for performing a color process to a color image signal upon forming an image on a recording medium in a digital copying machine, printer and the like.
2. Description of the Related Arts
There has been known a technique for performing a color matching process by utilizing a profile that describes a color characteristic of each device when a color management process is executed among different input and output devices, i.e., when a process is executed for reproducing almost the same color even by use of any input device or output device. The profile specified by the ICC is normally and popularly used as the standard of a profile for every device. The ICC profile is used for a color calibration, color proof and the like. In the conventional color calibration, it is used for a color conversion process from a printing machine, in which a color is desired to be matched, into a color printer for calibration.
In general, a color image signal given in the color calibration is a signal of a color space according to a printing machine to which the signal is outputted, so that CMYK color space is used, for example. Therefore, in the case of performing the color calibration, the color image signal of CMYK color space is once converted into a color image signal of a color space that is not dependent on the device, with the profile of the printing machine, and thereafter, it is converted into a color image signal of a CMYK color space that is dependent on the color printer, with the profile of the color printer for calibration.
Many of the profiles prepared for every device correspond to the case where a standard recording medium is used. An output device such as a printer is assumed, for example. Even when the same recording materials are used, a color reproducibility greatly differs depending upon a recording medium on which an image is formed. FIG. 15 is a graph showing a CMYK tone performance in a typical paper quality, while FIG. 16 is a graph similarly showing a color reproduction area. FIG. 15 shows a tone characteristic when tone representation is performed with a single color of each primary color C, M, Y and K, wherein the horizontal axis represents a color material amount (%) and the vertical axis represents a color difference ΔE from a white section of a sheet. As understood by referring to FIG. 15, it is found that a desired color development can not be obtained at a middle and high density area in the case of using uncoated paper compared to the case of using an art paper or coated paper. Further, as shown in FIG. 16, the reproducible color area is narrow in the uncoated paper, compared to the art paper, so that it is found that a bright color cannot be reproduced.
As described above, the tone characteristic and color reproduction area are different depending upon a paper quality. Therefore, there arises a problem that, even when color conversion is performed by use of a profile of a standard printing condition for forming an image, the reproduced color is different depending upon the used recording medium.
In order to perform a color conversion process considering a color reproducibility that is different per recording medium, it is necessary to use a profile that is established by considering the color reproducibility of the recording medium to be used. Accordingly, there arises a problem that a profile should be newly generated for performing color conversion when a printed matter printed on a recording medium other than a standard recording medium is desired to be color-matched to the other printed matters. The generation of a profile requires a profile creating application or an expensive measuring device, thereby entailing a problem that a color-matching cannot easily be executed.
Further, even if profiles each corresponding to each recording medium are prepared, plural profiles should be prepared corresponding to many recording mediums as for each profile according to each device or printing characteristic, so that the number thereof becomes enormous. Moreover, it is not easy to select a desired profile among such enormous profiles upon using profiles, thereby entailing a problem of being difficult to use these profiles.